It is known in the art relating to internal combustion engines, including vehicle engines, to provide a turbine in the exhaust system to draw power from the engine exhaust gases. The turbine may be used for driving various devices and may be connected through a suitable power train with the engine output shaft to supplement the engine power output, thus forming a so-called turbocompound engine. Probably, however, the most common use of engine exhaust turbines is for driving a compressor in the engine induction system to compress the engine inlet charge in the manner well known in turbocharged engines.
The use of turbochargers as a means of increasing the maximum power of an engine has been known for many years. Nevertheless, until recently turbochargers have seen only limited application in automotive passenger vehicles and light duty trucks, in which adequate power has been obtainable merely by installing an engine of suitable displacement. Recently, however, the trend toward reducing the size of vehicle engines to increase the average fuel economy of the vehicle fleet has resulted in increased interest in and use of turbochargers as a means for providing additional power and performance from smaller sized engine packages.
At the same time, requirements for increasing control of vehicle exhaust emissions have resulted in recent years in the widespread usage of engine exhaust treatment devices for passenger and light duty commercial automotive vehicles, the so-called catalytic converter located in the engine exhaust system currently being the most commonly used treatment device.
The combination of these factors has resulted in the recent appearance of a turbocharged engine powered automobile having a catalytic converter exhaust treatment device located in the exhaust system after, or downstream of, the exhaust turbine. In this position the treatment device operates normally, when raised to its elevated operating temperature level by the heat of the exhaust gases, to promote the conversion of undesirable constituents in the exhaust gases, such as hydrocarbons and carbon monoxide, to uncontrolled compounds such as carbon dioxide and water. It is recognized, however, that, as emission control standards become more stringent, it may be necessary to provide additional means of arrangements by which the exhaust treatment device is more quickly brought to its operating temperature during warm-up so that the desired control of exhaust emissions is more quickly established.